Aging Behavior of High-Strength Al Alloy 2618 Produced by Selective Laser Melting
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DOI: 10.1007/s11661-016-3883-y The Minerals, Metals & Materials Society and ASM International 2016
Additive manufacturing (AM) techniques allow the fabrication of objects starting from 3D digital models by direct or layer-wise addition of material. Among AM processes for producing metal parts, selective laser melting (SLM) is currently the most studied and employed method. SLM is based on local melting of a metal powder bed by a high-power laser beam.[1–4] Several processing parameters, including layer thickness, scanning strategy, hatch distance, spot size, focus
RICCARDO CASATI, JANNIS NICOLAS LEMKE, ADRIANNI ZANATTA ALARCON, and MAURIZIO VEDANI, are with the Department of Mechanical Engineering, Politecnico di Milano, Via G. La Masa 1, Milan, Italy. Contact e-mail: [email protected] Manuscript submitted July 12, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
position, and power of the laser, affect the incident energy, the geometry of melt pool, and the defect distribution.[5–7] The small size and the high energy density of the beam over the metal powder bed leads to high heating and cooling rates, rapid solidification, and large thermal gradients within the melt pool.[8] These phenomena are responsible for the formation of non-equilibrium phases, fine microstructures, and solid solubility extension.[9] The processing of Al alloys by SLM is particularly challenging because of the tendency to form tenacious oxide films, the high reflectivity and the high thermal conductivity of Al powder.[10] High-strength Al alloys containing Cu are even more difficult to process, owing to their tendency to segregate Cu-rich compounds during solidification, leading to hot-cracking phenomena.[11] On the contrary, Si-rich Al alloys, formerly developed for casting processes, offer good castability, reduced shrinkage, and low melting temperature imparted by a large volume fraction of Al–Si eutectic. Being also readily weldable, they are potentially suitable to be processed by SLM.[12] Several gas-atomized Al-based powders with optimal morphology and composition for SLM are already available on the market. Among them, alloys containing Si as main alloying element are the most popular, such as the AlSi12 and AlSi10Mg alloys. As shown by several authors,[13–17] full-dense AlSi10Mg parts can be produced by using high laser power. Al alloys are currently employed in AM for functional and structural parts that serve in industrial, automotive, and aerospace applications. In order to further diffuse the use of AM Al parts in high-performance structural applications, new high-strength alloys need to be more closely investigated. Several heat-treatable wrought Al alloys belonging to the 2XXX, 6XXX, and 7XXX series show superior mechanical properties at high and room temperature, and for this reason they are commonly adopted for producing high-performance application parts.[18] To the authors’ knowledge, most of these alloys have never been processed by AM. Apart from a few exceptions, only fragmented information was published on microstr
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